illustration: Mike Ellis

How the Zipper Merge Helps Traffic Flow

By Misty Harris

We’ve all been there. A sign warns of a lane closure ahead and you’re faced with two options: immediately merge into the bottleneck and secure your spot in line, or drive to the end of the closing lane before making your move—in front of drivers who waited their turn.

Both driver types—the “line-uppers” and the “cheaters”—tend to be equally convinced their way is best. The former because their behaviour seems polite and less stressful; the latter because their strategy leverages empty road real estate and saves time. But who’s right?

For years, the question has been up there with cilantro and the series finale of Lost in its ability to spark debate—especially during Alberta’s busy construction season. AMA’s driving experts, in line with traffic research, say the answer is the zipper merge.

Put simply, drivers use both lanes fully to the point of closure (or defined merge area), then alternate, zipper-like, into the open lane. The technique maximizes available road space, fostering fairness and courtesy when everyone abides by it. In fact, research shows it can reduce congestion by as much as 40 percent.

“As Canadians, it’s our natural instinct to line up and be patient. Nobody likes seeing other people race past them,” says Jeff Kasbrick, AMA’s vice-president of government and stakeholder relations. “But if all drivers use the zipper merge, all drivers benefit. In other words, if everyone is using both lanes equally, nobody is cheating.”


AMA’s endorsement in the media of this technique sparked a national conversation about merging, and Canadian motorists have shown a real passion for discussing best practices. We invest so much time behind the wheel, so it only makes sense to also invest in refreshing our driving knowledge and skills.

The case in favour of zipper merging comes down to efficiency and helping to ease congestion.

A recent CAA study concluded that bottlenecks are the single biggest contributor to road delays, far outpacing traffic collisions, weather and construction. In Calgary, for example, a pair of Crowchild Trail bottlenecks—at 24th Avenue and between University Drive NW and Memorial Drive NW—results in an additional 1.42 million kilograms of carbon dioxide emissions, 150,000 hours of driver delay and $4.34 million in lost productivity each year.

Learn the correct way to navigate traffic circles and roundabouts, and why merging is like an ethics test on the road

In Edmonton, a bottleneck on Gateway Boulevard—between Whitemud Drive and 34 Avenue—annually accounts for 966,000 kilos of carbon emissions, 92,000 hours of driver delay and $2.65 million in lost productivity.

A small change in thinking can make a huge difference. “Adopting the zipper merge is a way of making things better for drivers,” Kasbrick says. “It helps to ensure both lanes move at an equal pace and that we’re all being courteous to one another. Given that two-thirds of Canadians believe congestion is getting worse, every little bit helps.”

Tips for performing a safe and successful zipper merge (when conditions allow):

• Drive consistently. Don’t rush ahead, only to slam on your brakes later.

• When ready to move over, signal your intent and merge in an alternating fashion.

• If there is no bottleneck and an early merge makes sense, feel free to do so.

• The zipper merge works best in traditional congestion situations like construction zones. If a lane closure is due to a crash or breakdown, reduce your speed and move over as soon as possible to avoid endangering emergency workers and/or tow truck operators.